The present invention relates generally to wavelength division multiplexing and demultiplexing systems, and, more particularly, to optical add/drop multiplexing and related switching systems utilizing switched gratings.
With the advent of substantial new uses for electro/optic systems, there exists a greater need to effectively control the multiplexing and routing of signals that are Wavelength Division Multiplexed (WDM), and Dense Wavelength Division Multiplexed (DWDM), on optical fibers. A central operation required in managing such WDM and DWDM systems is the addition of signals into empty channels (Add) and selection of signals from populated channels (Drop). Each of these channels correspond to specific, predefined wavelength ranges in the wavelength division multiplexed signal stream. A typical signal in a given channel consists of a modulated optical carrier that has a center (carrier) frequency corresponding to a wavelength in that predefined wavelength range. The International Telecommunications Union (ITU) has defined grids of WDM channels each with a center frequency, frequency spacing between channels, etc.
For example, when a stream of n discrete wavelength channels are multiplexed on a single optical fiber, there is a need to selectively remove the signals from specific wavelength channels and to selectively add signals into specific wavelength channels to the data stream. The initial multiplexing of many different wavelength channels requires wavelength multiplexers. Similarly, wavelength demultiplexers (also, referred to, in the context of this application, as “drop” multiplexers) are often required to separate the different wavelength channels which are multiplexed in WDM systems. Such devices are needed, for example, in digital telecommunication systems and analog RF photonic systems, although, it should be realized that these are just two of numerous electro-optic systems which require the use of such devices.
Past approaches for optically multiplexing, demultiplexing, adding, or dropping optical signals of differing wavelengths have deficiencies associated therewith. These deficiencies include, but are not limited to, excessive insertion loss, expense and complexity, size, lifetime issues, and crosstalk. There is still much room for advancement in these prior approaches, particularly with respect to losses, complexity, crosstalk, switch isolation, compactness and multiple reflection suppression.
It is therefore an object of this invention to provide optical add/drop multiplexing systems which has superior switch isolation, multiple reflection and crosstalk suppression; less complexity and lower insertion loss; and less stringent wavelength tolerances than systems of the past.
It is another object of this invention to provide optical add/drop multiplexing systems which are extremely compact.
It is still another object of this invention to provide optical add/drop multiplexing systems which utilize switchable gratings therein.